A finished gate structure (such as a finished gate electrode or transistor gate) is the transistor terminal that modulates channel conductivity. Two principal approaches for forming semiconductor device gate structures are the gate-first and gate-last process approaches.
During fabrication of gate structures for, for instance, complementary metal-oxide-semiconductor (CMOS) technology, gate-first fabrication has traditionally been employed. In a gate-first fabrication approach, a conductor is provided over a gate dielectric, and then patterned and etched to form one or more gate structures. After forming the gate structures, source and drain features of the semiconductor devices are provided.
More recently, the gate-last approach (or replacement metal gate (RMG) approach) has been employed. In the gate-last approach, a sacrificial (or dummy) gate material is provided, patterned and etched to define one or more sacrificial gates. The one or more sacrificial gates are subsequently replaced with, for instance, corresponding replacement metal gates, that is, after source and drain features of the devices have been formed. The sacrificial gate material holds the position for the subsequent metal gate to be formed. For instance, an amorphous silicon (a-Si) or polysilicon sacrificial gate material may be patterned and used during initial processing until high-temperature annealing to activate the source and drain features has been completed. Subsequently, the a-Si or polysilicon may be removed and replaced with the final metal gate.
A goal of integrated circuit fabrication technology is to continue reducing the size of transistors, such as the metal oxide semiconductor field-effect transistors (MOSFETs) often employed in integrated circuits or semiconductor devices in order to reduce the size of the resultant devices and thereby provide higher performance, with lower power consumption. This goal includes continuing to provide enhancements to the above-noted gate fabrication approaches, including the gate-last processing approach for fabricating a gate structure.